The physical constitutions of vehicle occupants who wear seat belts are different to a considerable extent from one occupant to another. Accordingly, it is preferred from the viewpoint of safety that the length of each webbing and the mounting positions of its anchors (especially, the upper fitting for a shoulder webbing) are adjustable in accordance with the physical constitution of the occupant who wears the webbing. The webbing extends over the face or neck area of the occupant if the position of the upper fitting for the shoulder webbing is too high. On the other hand, the webbing passes over his arm instead of extending over his shoulder if the position of the upper fitting for the shoulder webbing is too low. Each of the above cases involves a potential danger that the webbing may not be able to protect the occupant effectively in the event of an emergency.
With the foregoing problem in view, a variety of adjustable upper-fitting mounting devices has been provided (see, for example, U.S. Pat. No. 4,225,185 issued Sept. 30, 1980 to Peter Krzok; U.K. Patent Specification No. 1,486,974 published Sept. 28, 1977 and naming Chrysler United Kingdom Limited as the applicant; U.K. Patent Application No. 2,081,568A laid open on Feb. 24, 1982 and naming Bayerische Motoren Werke AG as the applicant; U.K. Patent Application No. 2,078,092A laid open on Jan. 6, 1980 and naming P A Rentrop Hubbert & Wagner, Fahrzeugausstauttungen GmbH & Co. KG., etc.). Many of such prior art upper-fitting mounting devices include lock members provided integrally with the upper fittings. The upper fittings are displaced by pushing or pulling same so as to cause the lock members to fit in most suitable attachment holes. Mounting devices of the above sort are however accompanied by such drawbacks that they suffer from poor operability because they do not permit smooth height adjustment by one-touch action; and the lock members may be disengaged from their corresponding attachment holes because the lock members may be twisted together with the upper fitting if twisting forces are applied to the upper fittings in the events of emergencies such as vehicle collisions, overturns, etc. Some of conventional upper-fitting mounting devices of another type do not seem to be easy to handle for occupants sitting in the vehicles.